State of reactants and products

Tables of standard entlialpies of formation, combustion and reaction are available in the literature for a wide variety of compounds. It is important to note that these are valueless imlcss tlie stoicliiomctric equation and tlie standard state of reactants and products are included.

The states of reactants and products are often not given for organic reactions, because the reaction may take place at the surface of a catalyst or it may take place in a nonaqueous solvent, as here. The reaction is another example of an elimination reaction and is carried out in hot ethanol, with sodium ethoxide, NaCH CH,0, as the reagent. Some Cl I3CH2CH=CH2 is also formed in this reaction. 

In chemical reactions there is an electronic reordering in which some bonds are broken to form new ones. A full description of a chemical process thus requires the understanding of the electronic change involved since it will determine the main forces appearing along the process. Using the electronic states of reactants and products as a diabatic basis set representation, the reactions take place when... 

In reactions in which states of reactants and products are the same as below, 2NH3(g) N2(g) + 3H2(g)... 

In an equilibrium reaction, the states of reactants and products may be the same or different. If the states of reactants and products are the same, the equilibrium is called a homogeneous equilibrium. If they are different, then it is called a heterogeneous equilibrium. 

Fig. 25 State correlation diagram for an SN2 reaction. The lower states are ground states of reactants and products, while the upper states are the corresponding charge transfer states. P is the degree of avoided crossing. AE is the reaction barrier...

The transmission coefficient k — 1 for weak overlap of electronic states of reactants and products in the transition state. It is strong enough to be adiabatic but yet weak enough for the free energy of activation not to have an appreciable contribution from the resonance energy. This condition is almost fulfilled by outer sphere redox reactions at electrodes. 

Note that the physical states of reactants and products must be specified as solid (s), liquid (0, gaseous (g), or aqueous (aq) when enthalpy changes are reported. The enthalpy change for the reaction of propane with oxygen is A H = -2043 kj if water is produced as a gas but AEf = -2219 kj if water is produced as a liquid. 

In addition to specifying the physical state of reactants and products when reporting an enthalpy change, it s also necessary to specify the pressure and temperature. To ensure that all measurements are reported in the same way so that different reactions can be compared, a set of conditions called the thermodynamic standard state has been defined. 

Molecular beams, chemiluminescence and laser-induced fluorescence experiments show the theory in its simple form to be fundamentally flawed, with internal states of reactants and products and the redistribution of energy on reaction being of fundamental importance. 

The total rate of reaction, dnc/dt = —dnA/dt, is obtained from Eq. (2.11) by summing over all possible quantum states of reactants and products and all possible velocities vA and i>b- We find... 

Here V is the matrix element which describes the coupling of the electronic states of reactants and products, S is known as the electron-vibration coupling constant which is equal to the inner-shell reorganization energy X- expressed in units of vibrational quanta,... 

The physical states of reactants and products are included where necessary. The symbols used are (s) for solid, (/) for liquid, (g) for gas, and (aq) for aqueous (water) solutions. In the case of sodium chloride formation, the equation is modified accordingly. 

VBSCD Valence bond state correlation diagram. A VB diagram that views the barrier formation as a result of avoided crossing between two state curves that are anchored in the ground and two excited states of reactants and products. The VBSCD is a paradigm for the barrier in chemical reactions (see Chapter 6). 

The values of coordinates and velocities (or momenta) at some point in the reactant and product asymptote, respectively, can be used to define the boundary conditions for solving the equations of motion describing an elementary process (18,43). The coordinates Qk = Q, Q2 = Qi and velocities Vl = V, V2 = VJ2j at the end points refer to both the internal and translational degrees of freedom the choice of the end points thus determines the channel as well as the internal (quantized) and translational states of reactants and products. 

The chemical potentials in this equation refer to reactants at their original state before reaction and products at their final state after completion of the reaction. Therefore, the Gibbs function compares the two equilibrium states of reactants and products in between these states, the reaction may proceed at constant T and V in a steady or unsteady state. 

Correlation diagram A diagram which shows the relative energies of orbitals, configurations, valence bond structures, or states of reactants and products of a reaction, as a function of the molecular geometry, or another suitable parameter. An example involves the interpolation between the energies obtained for the united atoms and the values for the separated atoms limits. 

States of reactants and products in organic reactions are often not give because the reaction may take place on a catalyst surface or in a non-aqueous solvent, as in the reaction above. 

To give a more complete description of reactions, we indicate the physical states of reactants and products (g) for gases, (f) for liquids, and (s) for solids. The notation (aq) following ions indicates that they are hydrated in aqueous solution that is, they interact with water molecules in solution. The complete ionization of a strong electrolyte is indicated by a single arrow (—>). 

The study of chemical reaction rates is called chemical kinetics. Whereas thermodynamics deals with the relative energy states of reactants and products, kinetics deals with how fast a reaction occurs and with the chemical pathway (mechanism) it follow s. 

The value 572 kJ in these equations is 2 X 286 kJ, which is the amormt of energy released when 1 mol of liquid water forms. Note the use of the symbols (s), (1), and (g). When energy values are included with an equation for a reaction, it is especially important to show the states of reactants and products because the energy change in a reaction can depend greatly upon physical states. 

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